I use 12L14 for all my screws except a little one that holds the link to the mainspring and it is drill rod-0-1 and not hardened. The slot as has been stated should be a "V:with an acute angle. I have several of these files and my favorite for most small screws is a knife shaped 4" English made Stubbs Olympic #2 cut. These quality files are extinct as far as I know. I used to buy them in sets from a supplier in Columbus,Ohio called Stern,Inc. I am always looking for small files and tools but most of the flea markets around here are junk and rummage and new made junk from China.
Bob Roller